How can I make the red bricks on my fireplace look more vivid?

I think this can help you: https://www.hunker.com/13402089/how-to-improve-the-look-of-red-bricks-on-an-old-house

I would vacuum them to get the dust out if the brick, then leave them natural. Brick is porous so anything you do to them will soak in.

If you go to "explore projects" in top right, then "make over" or type in "fireplace surround" in "makeover" it will bring up many ways to do your bricks and various fireplace do overs. Here is one I found for you. If it is not exactly what you like, there are many more there. Hope this helps! https://www.hometalk.com/diy/living-room/fireplaces-mantels/fire-place-makeover-valspar-autumn-russet-4750266

Fire Place Makeover!

You can only benefit from use of red concrete colorant directly on the bricks if these are relatively new, and almost Hot Out of the Kiln, regardless of what the sites suggest.

Better methods exist that do not necessitate as much prep nor onset the undesirable result of: Colored Mortar Too.

Among the best methods is just to mix the Deep Red colorant into a Brick or Concrete Suitable Heat resistant Sealant to create a Colored Gloss or Laminate.

That rolls on Easily after you tape off the White Mortar with a Decent Painter's Tape and a Stencile Knife or Utility Knife.

That will endure and retain the Colors more vividly for years to come while also the sealant creating a Sheen to the surface makes it much easier to clean and maintain, no longer collecting fuzzes from the old tshirts.

Go easy on the additive like 1 part additive to 15 parts sealant, and try it in small splotches to see if you like the color.

For Pinkly: Parts+Parts2 will always sum 16, as 1:15, 2:14, 3:13, 4:12 and 5:11.

For Reddish: Parts+Parts2 will always be 36 as 6:30, 8:28, and 16:20 maximum.

Just know 12:36 does not equal 4:12 in hue even though stupid math suggests it will.

(It will in a 48 oz. bucket but not in a 16 oz. chemistry)

If you don't like the first Parts:Parts Mix do not give up, as it will sand off with sandpaper and you can add more additive as you like.

Keep in mind: the more colorant you add the more dull that sealant will get.

If the sheen gets dull you can always apply a Topcoat of the Heat Resistant Sealant.

Yourself as Female, will likely find something around the ratios of 3:13 to 10:26 is the Vivid you like best, and that should eliminate any need for a topcoat.

Men however will more go for the dull multiprocess related colors, deeper red (or brown colorant) closer to a range between 15:21 to 28:8 for the Bottom Dull Coat. To apply a Second Coat after that dries to effect a more Glossy Sheen.

Use gloves as you will not get this off your hands for a while.

We had a mason steam clean ours and spray on a sealant. It is not shiny but the colors are deeper and dust does not stick like it did on the bare brick.

I painted my fireplace with regular latex paint. I does soak up a lot of paint but all I wanted to washout the terrible pink-orange barf color. I brushed on the paint and wiped it back off. Enough color soaked in to change the color perfectly. I was surprised how quickly it was done.

Since you want to redden your brick, just add the paint to the center area of the bricks and avoid the mother. It's easier than it sounds.